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I have been reading up on intonation and compensation and it seems to be a rather complex topic.

I understand the issue of string diameters and stiffness and how that relates to intonation and compensation. The equation is certainly not linear. But almost all classical guitars have a saddle parallel with the bridge as if all strings need the same compensation. How do they get away with this? The angled saddle on a steel string makes more sense to me, but clearly, it is not done on a classical. Why not?

Furthermore, I think I understand why compensating the B string on steel string acoustic and electric instruments is the main focus: because the string demograhics change radically between 2nd and 3rd string. That radical change happens between the 3rd and 4th strings on a classical as that is where the strings transition from metal wound nylon fibers to solid nylon strands. But this gets hairy when classical players swap in a CF G string. It makes the situation seems convoluted, when it probably follows the same set of calculations and/or actual adjustment measurements. Please comment.

Thanks for any enlightenment you can offer!

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If thee meddle with dragon kin, thou will become crunchy and good with ketchup.

They get away with it because most players don't use the fifth and sixth strings up the neck in any context where you can hear if they are harmonizing nicely with the treble strings.
To compensate a bridge correctly is not all that difficult, but there is little point in doing it until the following are true:

The instrument has been played for a few years and is done warping to its hopefully final shape. It is the pull of the strings warping the neck, upper bouts, soundboard, really the whole guitar. All this causes the nut and the saddle to move a little closer together.

The player has definate opinions about the action and the strings that they like. The nut and saddle have been detailed to fit what the player really likes.

Any warps in the neck have been fixed by removing the frets and planing or sanding the fretboard.

An acoustic or classical guitar usually will need a two piece saddle. One piece for the plain strings and one for the wound ones.
They will both slant back. The amount of slant and the location of the saddles are not that hard to determine, but they will be specific to that guitar with its own action and strings. People who care enough to want a compensated saddle also care enough to have it done expertly to their instrument.
I have fitted two piece saddles to my own classic and steel-string guitars. It is really worth it.

Beware the internet.

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George :-)

The important factor in compensation is not stiffness, or even diameter, but how much the string stretches when you fret it. That's related to stiffness and diameter, of course, but that's secondary. If the string can stretch more, so that there's less rise in tension when you fret it, it needs less compensation. Nylon is stretchier than steel as a material: it has a much lower Young's modulus. All else equal a nylon string will need less compensation than a steel one. That's the general reason for the fact that nylon string guitars have not traditionally used much compensation.

The G string on most Classical guitars is the main exception. Steel string players generally use a wound G. Compared with a plain G it has a much thinner core that's easier to stretch than the thicker plain string, so it needs less compensation. If you put a plain steel string on your guitar for the G, you'll find that it 'bends' a lot easier, and needs more compensation. Nylon string players don't like wound third strings. Partly it's because they 'zip' more with position changes: that's more a matter of the player's technique than anything else, but they seem to feel they've got other bigger problems and don't want to put in the effort. More to the point, though: the few wound nylon G strings I've seen are wound with thin plastic or nylon, and it wears very quickly. They sound great, but not for long.

Classical players have been paying more attention to compensation in the past few years, and it's becoming pretty common to compensate saddles, and even nuts, on Classical guitars. One problem with that is that 'nylon' is a class of materials, rather than something specific, like steel. Every string maker seems to use something different, to get 'their' sound, I suppose, and they all stretch differently. Thus the proper compensation for one set of nylon strings can be quite different from that for another set from a different manufacturer. Some players like to try out different brands of strings to get a particular sound, and even mix and match strings from different sets, and this plays hob with the intonation until they settle on something.

lolz - I was actually reading the Cumpiano book. But I would agree that knowledge can be a curse in certain maladaptive quantities...

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If thee meddle with dragon kin, thou will become crunchy and good with ketchup.

So that means the important thing is longitudinal stiffness, right? .


Depending on how picky you are, they don't. The variation in longitudinal stiffness across a good set of "nylons", though, is a lot less than the variation in stiffness across a set of steel strings. For example, the cross-sectional area of a 0.016" B string is about twice that of a 0.012" E string, which means it has twice the longitudinal stiffness and if dealing only with saddle compensation, means it will need about twice the compensation.

No one I know uses CF strings. Fluorocarbon, yes, which has a similar stiffness (at the diameters used) to "nylon" otherwise they couldn't be interchanged. But fluorocarbon is getting on for twice the density of nylon, so is generally run at lower diameters and higher tensions than nylon (and the lower diameter and consequential increase in high harmonics and reduced damping is why it is a favoured material for the 3rd string)

You can probably figure out where "chapter and verse" on all this stuff is, if you are interested in the detail.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

The bending stiffness of a string, so far as I know, is proportional to the fourth power of the diameter, while the 'stretchiness' is related to the cross sectional area, which is a function of the square of the diameter, all else equal. If I understand this correctly, bending stiffness affects the inharmonicity of the strings, but not the compensation directly. Since I've loaned out my copy of 'the book' I can't look it up at the moment.

Alan, what you are calling "stretchiness" IS Longitudinal Stiffness.

Your memory serves you well, Alan!

Exactly. The longitudinal stiffness has a lot to do with the intonation problem, whereas bending stiffness has very little to do with it (but a lot to do with inharmonicity).

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

! My bad: I tend to think of 'stiffness' in terms of bending, but you're right. That's what I get for posting without thinking.